WHEN MOVIE STAR Julia Roberts erupts with her ear-to-ear
megawatt laughter, we really love it. We all express ourselves
in many ways, but laughter is the most enjoyable, peculiar and
mysterious phenomenon.

Sounds of laughter are all around us. They are so pervasive
that we tend to dismiss them. It is hard to believe that
laughter can be a subject of serious scientific research.

Why do we laugh?

It is commonly understood that we laugh in response to
jokes. But that's not absolutely correct.

Based on an analysis of 1,200 laughter episodes, psychology
professor Robert Provine, of the University of Maryland,
concludes that 80 per cent of laughter has nothing to do with
humour.

In fact, we laugh at all occasions: we laugh when we are
nervous, excited, tense, happy, tricked by someone, or simply
because someone else is laughing or crying.

Doris Bergen, professor of educational psychology at Miami
University in Oxford, Ohio, says that while laughter is an
innate characteristic, our reasons for laughing vary at
different ages. Children, for example, laugh unconditionally
while adults laugh for some reason or purpose.

Babies start giggling as a result of physical interaction
from games such as peekaboo. Even at that early age, a baby
laughs if she anticipates her father approaching her, but
watches him tumbling and falling down.

When children get to preschool age, they begin
understanding riddling patterns. They laugh at riddle-telling,
regardless of whether they understand the point of the riddle.

Young children are estimated to laugh over 300 times a day
- a reason why they seem to have more obvious fun than adults
who average 20 times daily.

Not so long ago, laughter was considered an unsocial,
sinister behavior. In the eighteenth century, Lord
Chesterfield, writing to his son, said, ". . . there is
nothing so illiberal, and so ill-bred, as audible laughter."

According to Oliver Goldsmith, laughter was the expression
of "the vacant mind" and John Ray likened it as "the hiccup of
a fool."

Today we have come a long way. Laughter is accepted as a
natural, social behaviour. In fact, having a good sense of
humour is regarded as a thoroughly desirable attribute by
almost all of us, including human resource managers.

Recent surveys indicate that laughter can enhance the
quality of our conversations and productivity. It makes people
feel closer to each other.

In his book, Laughter: A Scientific Investigation, Provine
says that laughter is the oil in the social machine, helping
human interactions run more smoothly.

Provine reveals laughter is 30 times less likely to occur
when a person is alone than when a person is with others.

We tend to think of laughter as being tee-hee or ha-ha or
ho-ho sorts of sounds, but studies conducted by Vanderbilt
psychologist Jo-Anne Bachorowski and Cornell psychologist
Michael Owren indicate otherwise: laughers produce many
different kinds of sounds, including grunts and snorts.

Bachorowski and Owren studied the way 97 young adults laugh
in different kind of social pairings as they watched humorous
scenes from films such as When Harry Met Sally or Monty Python
and the Holy Grail.

In their research, published in the September 2000 issue of
the Journal of the Acoustical Society of America, the
investigators found interesting gender differences in laughter
sounds, with males tending to grunt and snort more often than
females.

Women produced more musical laughter than men. These
song-like laughs are "voiced," meaning that they involve the
vocal folds, the tissues in the larynx involved in producing
vowels and related sounds.

On average, men and women produced the same number of
laughs, but men tended to laugh a "bit longer" than women.

A person's laughter was found to be dependent on the sex of
his or her companion. When paired with friends of either sex,
men laughed significantly more than men who were tested alone
or with a male or female stranger.

Women, one the other hand, produced more laughs in the
company of a male friend than females tested alone, with a
female friend, or with a male stranger.

Laughter is greatly influential. In a study presented at
the 138th Acoustic Society of America meeting, Bachorowski and
Owren studied the impact that laughter sounds have on
emotional responses in listeners.

In a quite room, undergraduate students listened to a set
of 70 laughs over headphones. Fifty of the laughs (25 produced
by males and 25 by females) were voiced. The remaining 20
laughs (10 produced by males and 10 by females) were unvoiced,
sounding more like pants or cackles.

The students were asked to rate the laugh samples in terms
of their friendliness, sexiness, how interested they would be
in meeting the laugher, whether they thought the laugh should
be included in a laugh track, and the extent to which it
elicited a positive emotional response.

Regardless of the rating scheme, the researchers found that
listeners were more likely to rate comparatively
stereotypical, song-like laughs more positively than the other
types.

"These results support the notion that one important
function of laugh acoustics is to influence the emotional
responses of listeners," the researchers conclude.

The science of laughter is in its infancy, but one thing is
clear: laughter is good you.

Laughter stimulates our endocrine system, including the
pituitary gland. The pituitary gland, in turn, stimulates
release of endorphins and enkephalins, natural painkillers
that are chemical cousins to opiates such as morphine and
heroin.

Dr. Lee S. Berk, at Loma Linda University School of
Medicine and Public Health in California, and endocrinologist
Stanley Tan studied groups of average adults and found that
both arms of the immune system got a boost out of laughter.

Participants faced a solid hour of videos of comedians,
while a control group sat quietly out of earshot. The
researchers took blood samples at 10-minute intervals before,
during and after the laughter workout.

The laughter group showed increases in the good hormones -
such as endorphins and neurotransmitters, and decreased levels
of the stress hormones - such as cortisol and adrenaline.

Laughter also creates an increase in the number and
activity level of natural killer cells, which attack
virus-infected cells and some types of cancer cells. Laughter
can also keep allergies at bay. According to a report in the
Journal of the American Medical Association, Dr. Hajime Kimata
of Unitika Central Hospital, Japan, studied the effects of
laughter on patients allergic to dust mites, cedar pollen and
cat dander.

Skin prick tests using a commercial allergen were performed
on 26 patients before and after they viewed the Charlie
Chaplin comedy Modern Times. During the same procedure, a
control group watched a video featuring weather information.

The results showed that allergic reactions of comedy
watchers were reduced for four hours after the screening. In
contrast, there was no effect on allergic responses of weather
watchers.

Laughter, along with an active sense of humour, may also
help protect against heart attacks, according to a study by
cardiologists at the University of Maryland Medical Center in
Baltimore.

The researchers found that people with heart disease were
40 per cent less likely to laugh in a variety of situations
compared to people of the same age without heart disease.

An old saying puts laughter in its true perspective and
spirit: "He who laughs, lasts."